Cytokeratins are cytoskeleton proteins of epithelial tissues, contributing to the mechanical stabilization of the cells. The cytokeratin family consists of at least 20 isotypes, which are largely specific for particular organs or tissue types. Therefore, immunohistochemical staining of cytokeratins is clinically used for diagnosis of carcinomas, in particular of unclear metastases and in precise classification and subtyping of tumors (1). Cytokeratin 7 (CK7) is expressed in healthy bladder, in the female genital tract epithelium, in mesothelium and in the lung (2). In tumors, CK7 expression is found in the majority of carcinoma types, with the exception of those carcinomas arising from the colon, prostate, kidney and thymus (3). Furthermore, CK7 expression can have prognostic relevance, e.g. adverse prognostic factor in lung cancer (4), or predictive relevance, e.g. predictive factor of response to concurrent radiochemotherapy in advanced cervical cancer (5).